Lasers are useful in medical, materials processing, and other applications to cause ablation, i.e., substance removal, within a substrate, e.g., a biological tissue. In many cases, lasers cause such ablation by rapidly and locally heating a target substance until the target substance vaporizes.
Selective laser ablation can be accomplished by using laser wavelengths that are strongly absorbed by the target tissue and only weakly absorbed by other tissue. Thus, the target tissue absorbs an amount of laser energy above a threshold for laser ablation and is removed, whereas the other tissue absorbs an amount of laser energy below the threshold and remains. However, few medical lasers and delivery systems currently available operate at wavelengths that are absorbed substantially more by some types of tissue and not by other types of tissue.
The invention features a system for selectively delivering or coupling laser radiation into a first material or substrate, e.g., a first biological tissue, having a first index of refraction and not into a second material or substrate, e.g., a second biological tissue, having a second index of refraction. The system determines whether a target area corresponds to the first material or the second material by monitoring the reflection of a probe beam incident on the target area through an optical coupler at a non-normal incident angle. For example, the incident angle can be less than the critical angle for total internal reflection for an interface between the optical coupler and the first material, and greater than the critical angle for total internal reflection for an interface between the optical coupler and the second material, in which case transmission of the probe beam is much greater when the optical coupler contacts the first material than when the optical coupler contacts the second material, and similarly, reflection of the probe beam is much greater when the optical coupler contacts the second material than when the optical coupler contacts the first material, with respect to reflection. The monitored reflection of the probe beam is the control signal for a feedback controller that causes a treatment beam to be delivered to the target area based on the monitored reflection. Thus, the control system selectively delivers the treatment beam to the target area when the optical coupler for the probe beam contacts the first material, but not the second material, or vice versa.
The treatment beam is at a wavelength and has sufficient energy to cause photophysical or photochemical change at the target area. For example, the treatment beam can be used to selectively remove fat-containing tissue from a target area. Fat-removal can be important in procedures such as laser liposuction, laser angioplasty, and dissection of fat. The laser energy delivered to the selected tissue by the treatment beam can rapidly heat the selected tissue until it vaporizes, thereby removing, ablating, or killing the selected tissue. Alternatively, the laser radiation delivered to the selected tissue can rapidly heat the selected tissue until it melts. Thereafter, the melted tissue is removed using suction or other methods.
Furthermore, rather than having an active feedback control system in which reflection of a probe beam incident on the target area at a non-normal angle controls the delivery of a treatment beam to the target area, the treatment beam itself can be delivered to the target area (though an optical coupler) at a non-normal incident angle. The incident angle is selected such that the treatment beam substantially reflects from the target area if the tissue therein is a first type of material (e.g., muscle-containing tissue) having a first refractive index and substantially couples into the target area if the tissue therein is a second type of material (e.g., fat-containing tissue) having a second refractive index greater than the first refractive index. In such examples, the treatment beam functions as both a probe beam selectively coupling into one type of material and not another, and a treatment beam causing photophysical or photochemical change when coupling into a material. Thus, the invention features both active and passive control systems for selectively delivering or coupling laser radiation into a first material or substrate and not a second material or substrate.
In general, in one aspect, the invention features a method for selectively delivering a treatment beam to portions of a substrate having a first index of refraction and not to other portions of the substrate having a second index of refraction less than the first index. The method includes: providing an optical coupler having an index of refraction greater than the second index of refraction; contacting the substrate with the optical coupler to deliver a probe beam from the optical coupler to the substrate at an incident angle; and selectively delivering the treatment beam to the region based on the reflectance of the probe beam from the substrate or the transmission of the probe beam through the substrate.
The method can include any of the following features.
The incident angle can be less than the critical angle for an interface between the optical coupler and a material having the first index of refraction and greater than the critical angle for an interface between the optical coupler and a material having the second index of refraction. The incident angle can be greater than about 10xc2x0, 20xc2x0, 30xc2x0, or 40xc2x0. The incident angle can be selected such that when the probe beam is incident on the substrate at the incident angle, the reflectance of the probe beam from an interface between the optical coupler and the portions of the substrate having the first index is at least twice, or at least four times, the reflectance of the probe beam from an interface between the optical coupler and the portions of the substrate having the second index. The optical coupler can have an index of refraction greater than the first index of refraction.
The treatment beam can have a wavelength different than that of the probe beam. The treatment beam can have a power greater than that of the probe beam. The substrate can absorb more strongly at the wavelength of the treatment beam than at the wavelength of the probe beam. The treatment beam can be delivered to the substrate through the optical coupler. The treatment beam can be selectively delivered to the region based on the reflectance of the probe beam from the substrate. For example, the treatment beam can be delivered to the region when the reflectance is less than about 0.95, less than about 0.9, less than about 0.8, or less than about 0.7.
The substrate can be biological tissue. For example, the portions of the substrate having the first index can include fat, e.g., they can consist essentially of fat. Alternatively, or in addition, portions of the substrate having the second index can include one or more of muscle, blood vessels, and skin, e.g., they can consist essentially of one of muscle, blood vessels, and skin. The power of the treatment beam can be sufficient to melt or ablate the portions of the substrate having the first index, and it can be delivered to the substrate at normal incidence. Each of the probe and treatment beams can be derived from a Nd:YAG laser, CTE:YAG laser, ErCr:YSGG laser, holmium laser, erbium laser, CO2 laser, diode laser, or dye laser. The probe beam can also be derived from a light emitting diode. The optical coupler can be made from one of sapphire, fused silica, BK-7 glass, fint glass, germanium, and zinc selenide.
In another aspect, the invention features a system for selectively delivering a treatment beam to portions of a substrate having a first index of refraction and not to other portions of the substrate having a second index of refraction less than the first index. The system includes: an optical coupler having a surface configured to contact the substrate and a refractive index greater than the second index; a probe beam source configured to direct a probe beam into the optical coupler to contact the surface at an incident angle; a detector configured to measure the reflectance of the probe beam from the surface or the transmission of the probe beam through the surface; a treatment beam source for the treatment beam; and a controller which during operation causes the treatment beam source to selectively deliver the treatment beam to the substrate based on the reflectance or transmission measured by the detector.
The system can include any of the following features.
The incident angle can be less than the critical angle for an interface between the optical coupler and a material having the first index of refraction and greater than the critical angle for an interface between the optical coupler and a material having the second index of refraction. For example, the incident angle can be less than the critical angle for an interface between the optical coupler and a material consisting essentially of fat and greater than the critical angle for an interface between the optical coupler and another material consisting essentially of one of muscle, blood vessels, and skin. The incident angle can be greater than about 10xc2x0, 20xc2x0, 30xc2x0, or 40xc2x0.
The incident angle can be selected such that when the probe beam is incident on the surface of the optical coupler configured to contact the substrate at the incident angle, the reflectance of the probe beam from an interface between the optical coupler and the portions of the substrate having the first index is at least twice, or at least four times the reflectance of the probe beam from an interface between the optical coupler and the portions of the substrate having the second index. For example, the incident angle can be selected such that when the probe beam is incident on the surface of the optical coupler configured to contact the substrate at the incident angle, the reflectance of the probe beam from an interface between the optical coupler and a material consisting essentially of fat is at least twice, or at least four times, the reflectance of the probe beam from an interface between the optical coupler and a material consisting essentially of one of muscle, blood vessels, and skin.
The refractive index of the optical coupler can be greater than the first index. The treatment beam source can be configured to direct the treatment beam to the substrate through the optical coupler. The treatment beam produced by the treatment beam source can have a wavelength different than that of the probe beam produced by the probe beam source. The treatment beam produced by the treatment beam source can have a power greater than that of the probe beam produced by the probe beam source.
The optical coupler can be made of one of sapphire, fused silica, BK-7 glass, fint glass, germanium, and zinc selenide. Each of the probe and treatment beam sources can be a Nd:YAG laser, CTE:YAG laser, ErCr:YSGG laser, holmium laser, erbium laser, CO2 laser, diode laser, or dye laser. The probe beam source can also be a light emitting diode.
In general, in another aspect, the invention features a probe for selectively delivering laser radiation to a first substrate (e.g., biological tissue) having a first index of refraction relative to a second substrate (e.g., biological tissue) having a second index of refraction less than the first index. The probe includes a laser transmitting medium including an optical axis and a substrate-contacting, e.g., tissue-contacting, surface. The optical axis contacts the tissue-contacting surface at an angle that is less than the critical angle for an interface between the tissue-contacting surface and the first tissue and greater than or equal to the critical angle for an interface between the tissue-contacting surface and the second tissue, wherein during operation the probe directs the laser radiation along the optical axis to the tissue-contacting surface.
In another aspect, the invention features an additional probe for selectively delivering laser radiation to a first tissue having a first index of refraction relative to a second tissue having a second index of refraction less than the first index. The probe includes a laser transmitting medium including an optical axis and a tissue-contacting surface, the optical axis forming an angle with the tissue-contacting surface. During operation, the probe directs the laser radiation along the optical axis to the tissue-contacting surface, transmits a first amount of laser energy through the tissue-contacting surface when contacting the first tissue, and transmits a second amount of laser energy through the tissue-contacting surface when contacting the second tissue. The angle is selected such that the first amount of laser energy is at least twice, and in some embodiments at least four times, the second amount of laser energy.
Embodiments for either of the probes described above can include any of the following features.
The angle can be substantially equal to a principle angle for optimal transmission when the tissue-contacting surface contacts the first tissue. The first tissue can consist essentially of fat and the second tissue can consist essentially of muscle, blood vessels, or skin. The first index of refraction can be greater than 1.4 at the wavelength of the laser radiation.
The probes can further include an optical fiber defining the optical axis, wherein during operation the fiber directs the laser radiation to the tissue-contacting surface. The probes can further include a prism connected to an end of the optical fiber, wherein during operation the fiber directs the laser radiation into the prism through a first face of the prism and towards a second face of the prism, the second face of the prism forming the tissue-contacting surface. In some embodiments, the laser radiation reflected from the second face of the prism can propagate along a path within the prism that is substantially normal to a third face of the prism having a reflective coating. In other embodiments, the probes can further include a second fiber, and the second and one or more additional faces of the prism direct laser radiation reflected from the second face to the second fiber, which carries the reflected radiation away from the prism.
The invention also features an apparatus that includes the probe and a laser radiation source coupled to the probe for delivering the laser radiation to the probe. The laser radiation source can include a diode laser, Nd:YAG laser, CTE:YAG laser, ErCr:YSGG laser, holmium laser, erbium laser, CO2 laser, or dye laser.
In a further aspect, the invention features a method for selectively delivering laser radiation to a first tissue relative to a second tissue in which the first tissue has a first index of refraction and the second tissue has a second index of refraction that is less than the first index of refraction. The method includes contacting the first tissue in the patient with a probe; and delivering the laser radiation to the patient through the probe at a first angle of incidence greater than the critical angle for an interface between the probe and the second tissue.
The method can further include redirecting laser radiation reflected from the first tissue or second tissue in the patient back to the tissue at a second angle of incidence substantially equal to the first angle of incidence. Alternatively, the method can further include directing laser radiation reflected from the first tissue or second tissue in the patient away from the patient.
In another aspect, the invention features an additional method for selectively delivering laser radiation to a first tissue in a patient relative to a second tissue in which the first tissue has a first index of refraction and the second tissue has a second index of refraction that is less than the first index of refraction. The method includes contacting the patient with a probe; and delivering the laser radiation to the patient through the probe at an angle of incidence such that the energy transmitted into the first tissue when the probe contacts the first tissue is at least twice, and in some embodiments, at least four times, the energy transmitted into the second tissue when the probe contacts the second tissue.
Biological tissue is solid tissue from, or in, a human, animal, or plant. Fat-containing tissue is biological tissue characterized by a relatively high lipid concentration including, for example, subcutaneous fat, lipomas, liposarcomas, arteriosclerotic fat, granulomas, xanthelasmas, xanthomas, intraperitoneal fat, and retroperitoneal fat. Biological tissue that contains little or no fat includes, for example, muscle, skin, blood vessels, other organs, and cartilage. At some wavelengths, the refractive index of other tissues, e.g., bone, teeth, and calculi (stones), is greater than that of fat. When desired, embodiments of the invention can be used to selectively affect, e.g., ablate, these high-index tissues.
The critical angle xcex8c for a probe/substrate interface is defined by xcex8c=sinxe2x88x921(nxe2x80x2/n), where n is the refractive index of the probe, nxe2x80x2 is the refractive index of the substrate, and the substrate can be absorbing or non-absorbing. In the latter case, the critical angle corresponds to the angle for total internal reflection (TIR).
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
The inventions have many advantages. For example, the systems can selectively deliver or couple laser radiation to biological tissue. Thus, selected tissue, e.g., fat-containing tissue, can be ablated or melted, while adjacent tissue, e.g., muscle, is left unharmed. Also, the system can be used in a large number of surgical procedures, e.g., open surgery, subcutaneous procedures, endoscopic procedures, catheter procedures, and arteriosclerotic procedures. Furthermore, since there are many wavelengths at which different types of biological tissues have substantially different indices of refraction, the system can be used with many readily available laser sources that operate at such wavelengths. For example, to distinguish certain biological tissues from others, the system can be used with a holmium laser operating at a wavelength of 2.1 microns, a diode or dye laser operating in the visible to near-infrared region, a CO2 laser operating in the infrared region, an Er:YSGG laser operating at a wavelength of 2.79 microns and other erbium lasers operating between wavelengths of 2.5 and 3.0 microns, thulium lasers operating at wavelengths between 1.94 to 2.01 microns, a CTE:YAG laser, and a ErCr:YSGG laser, the latter two lasers operating at wavelengths of about 2.7 microns.
There are also particular advantages to each of the passive and active aspects of the go invention. For example, in some ways the passive system is simpler because only a single beam is necessaryxe2x80x94that beam functioning as both the probe and treatment beam. However, there are also many advantages to the active system. For example, because the probe beam is used only to distinguish one type of tissue from another, but not used to cause photophysical or photochemical change in the target area, it can be less intense than it would need to be were it to also function as the treatment beam. As a result, when the probe beam is reflected from the target area, that reflected beam is more easily dissipated, thereby improving safety.
Moreover, by having separate probe and treatment beams, their respective wavelengths (and thus the choice of laser source to provide them) can be independently optimized. In particular, the wavelength for the probe beam can be chosen to correspond to refractive indices that optimize the difference in reflection or transmission between the materials to be distinguished, without concern for whether laser radiation at that wavelength is suitable for causing any photophysical or photochemical change in at least a selected one of the materials. Conversely, the wavelength for the treatment beam can be chosen to cause the desired photophysical or photochemical change in at least a selected one of the materials, without concern for whether the refractive indices corresponding to that wavelength are suitable for distinguishing the different material that may be present in the target area.
Finally, the active control system permits the treatment beam to be selectively delivered to a first material having a first refractive index, and not a second material having a second refractive index, even when the first refractive index is less than the second refractive index.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.